Reduction of armature rebound in crossbar switch units

ABSTRACT

Unstable rebounding or vibration of the armature of a crossbar switch is at least substantially reduced by positioning stops approximately at the ends of the armature, instead of at the centre as hitherto. The stops can be mounted on the outer legs of the core or frame and engage with the ends of the armature. This prevents rotation of the armature about a central pivot point, as can occur with a central stop.

United States Patent 1191 Roslin REDUCTION OF ARMATURE REBOUND IN CROSSBAR SWITCH UNITS [75] Inventor: Victor Oscar Roslin, Islington,

Ontario, Canada [73] Assignee: Bell-Northern Research IQtd.,

Ottawa, Ontario, Canada 22 Filed: Sept. 6, 1973 21 Appl. No.: 394,564

52 u.s.c1...- ..33s/271,33s/ 277 [51] 1m. (:1. ..n01r 7/0s [58] Field ofSearch 335/270, 271,277, 276, 335/274 [56] References Cited UNITED STATES PATENTS 6/1917 Palmer et al 335/270 x June 18, 1974 3,374,451 3/1968 Barker 335/112 3,701,066 10/1972 Bosch 335/274 Primary Examiner-George Harris Attorney, Agent, or Firm-Sidney T. Jelly ABSTRACT Unstable rebounding or vibration of the armature of a crossbar switch is at least substantially reduced by positioning stops approximately at the ends of the armature, instead of at the centre as hitherto. The stops can be mounted on the outer legs of the core or frame and engage with the ends of the armature. This prevents rotation of the armature about a central pivot point, as can occur with a central stop.

4 Claims, 7 Drawing Figures PAIENTEaJun 181914 3.818.397

' sum 1 or 2 Q 9 "x (CD O o 25 A?) |2 Fig. I PRIOR ART REDUCTION OF ARMATURE REBOUND IN CROSSBAR SWITCH UNITS This invention relates to the reduction of armature rebound in crossbar switch units.

In conventional crossbar switch units, a back-stop is provided to limit travel of the armature on release by the actuating coil. This backstop is approximately at the center of the armature but is often not symmetrical with the loads on the armature. The annature often pivots about this back-stop, giving unstable operation. Such operation can result in undesirable contact remakes, rebreaks and other undesirable conditions.

The present invention provides back-stops or stabilizers positioned to prevent as far as possible any unstable rebounding or vibration of the armature. The invention will be readily understood by the following description of certain embodiments, by way of example, in conjunction with the accompanying drawings, in which:

FIG. 1 is a plan view of a vertical unit of a crossbar switch in accordance with the prior art;

FIG. 2 is a partial plan view of a vertical unit of a crossbar switch embodying the present invention;

FIG. 3 is an end view of the unit of FIG. 2;

FIG. 4 is a side view of the unit of FIG. 2;

FIG. 5 is a perspective view of the unit of FIGS. 2, 3 and 4;

FIG. 6 is a diagram illustrating the relative positions of forces acting on the armature of the unit of FIGS. 2 to 5; and

FIG. 7 is a perspective view of one alternative embodiment of the invention.

FIG. 1 illustrates a crossbar switch unit, as at present used, and referred to generally as a MINIBAR switch vertical unit. The switch unit has an E-shaped corel0 which also functions as a main support frame. The core has two outer legs 11 and 12 and a central leg 13 on which is mounted a coil 14. Terminals 15 serve to connect an electrical supply to the coil 14. Extending across the open side of the E-shaped core is an armature 16. The armature is supported on the outer end of the central leg 13 by a flat spring 17. Spring 17 is attached to the end of leg 13 by a screw 18 and is spot welded or otherwise attached to the armature 16. Thus the armature is flexibly supported relative to the core or frame 10. Energization of the coil 14 creates a magnetic field which actuates the armature 16 toward the central leg 13 and outer legs I] and 12. De-energizing the coil 14 releases the armature.

On release, the armature I6 is urged to a position away from the core or frame 10 by return springs 20. Attached to and supported by the core or frame 10 are a series of banks of crosspoint card springs 21. There is also an additional group of hold off normal contact springs 22. Springs 22 are always actuated by the armature and therefore forces from these springs always provide a return force on the armature. In operation a select bar -not shownactuates spring fingers 23 so that the armature will act on one or more of the fingers 23 to operate one or more banks of springs 21, as well as the springs 22. Any bank of springs operated by the armature also produces a return force on the armature. It will be seen that it is not likely that return forces would be symmetrical about a central axis. An indication of typical return forces acting on an armature is illustrated in FIG. 6 in relation to the novel arrangement illustrated in FIGS. 2 to 5.

The switch unit is provided with a central stop. This is seen in FIG. 1, the stop 25 being an extension or flange formed on the end of the former or bobbin for the coil 14. When the armature is released -on deenergization of the coil 14, the armature strikes the stop 25. As the return forces are invariably nonsymmetrical, the armature tends to pivot about the stop and undesirable vibrations result. The armature is un stable and'in many instances the vibrations are such that undesired contact remakes and rebreaks occur.

FIGS. 2, 3, 4 and 5 illustrate a switch unit in accordance with the present invention. FIG. 2 is similar to that of FIG. 1 except that not all of the unit is shown. The same references are used for the same details. Basically the unit of FIG. 2 is the same as that of FIG. 1, with core or frame 10 having outer legs 11 and 12 and a central leg 13. A coil 14 is positioned on the central leg and armature 16 is supported on the end of leg 13 by the flat spring 17. Return springs 20 and spring contact banks 21 and 22 also are carried by the core or frame 10. Thus far the arrangement of FIG. 2 is as that of FIG. 1. However in FIG. 2 there is no stop 25 on the end of the former or bobbin for the coil 14.

Two armature stops 30 and 31 are provided in the arrangement'illustrated in FIG. 2, and also FIGS. 3, 4 and 5. These stops are attached to the outer legs of the core or frame 10, stop 30 on leg 11 and stop 31 on leg 12. As seen in FIG. 4, a stop 30 or 31, is of cranked form and is attached to its related leg 11 or 12, by a screw 32. The stops are positioned so as to overlap the edge of the armature remote from the fiat spring 17. Generally the stop just contacts the armature when it is in its fully returned position and is at rest, although this position may be modified to vary the damping action.

FIG. 6 illustrates, somewhat diagrammatically the various forces which can act variously on an armature 16. The return forces provided by the return springs 20 are indicated by arrows 20a. Similarly the forces provided by the crosspoint card springs are indicated by arrows 21a and the force due to the holding off normal springs 22 by arrow 22a. As explained previously forces represented by the arrows 20a and 22a are usually always present on the armature when closed. There will be some variation in the forces represented by the arrows 21a. They may occur at l, 2 or 3 points along the length of the armature depending upon the code of the switch. Thus the forces acting on the armature are almost certainly to be non-symmetrical about the armature centre.

The position of the backstop in present switch units is indicated by the arrow 25a. It will be appreciated that assymetry of the forces acting on the armature will cause the armature to pivot -or vibrate-about a point at the arrow 25a. Such movement is liable to cause remaking or rebreaking of contacts on the holding off normal spring bank 22 after the contacts have been broken or made by actuation of the armature as the case may be. It is possible for the armature to bounce or vibrate for three relatively large cycles or oscillations of movement at each end before the armature stabilizes at an off or released position.

The positions of the stops 30 and 31 of units in accordance with the present invention, and of the forces applied by the stops on the armature, are indicated by the arrows 30a and 310 respectively. With this arrangement, assymetrical forces will normally cause one end or the other of the armature to contact the related stop 30 or 31. Thus, for example as seen in FIG. 6, the annature 16 is shown in full outline in the operated position and in dotted outline one possible mode of release with one end in contact with stop 30 -indicated by arrow 30a. From this position the amiature 16 will then pivot about its contact position with stop 30 until the other end contacts the stop 31 -indicated by arrow 31a. The forces acting on the armature tends to keep it in contact with stop 30, resisting rebound. Similar conditions arise if the armature contacts stop 31 first. It has been found that often only one cycle or oscillation of .the armature may occur, with amplitude less than that often occurring for more than one oscillation with present switches. Even when more than one oscillation of the armature occurs, with stops in accordance with the present invention, the amplitudes in units according to the present invention are considerably reduced compared with present switch units.

Other ways of providing stops at the end of the armature can be used. Thus, instead of stops attached to the core or frame and overlapping the armature, as illustrated in FIGS. 1 to 5, it is possible to provide extensions on the armature, at each end, which will engage parts of the core or frame or which will engage a spring or springs or other forms of stops attached to the core or frame. One such arrangement is illustrated in FIG. 7. An extension 35 is attached to the underside of the armature l6 and engages with a part 36 on the core or frame 10. An extension 35 is provided at each end of the armature and a part 36 on each outer leg 11 or 12 of the core or frame 10. g

This invention provides a considerable improvement in the control of armature rebound and provides a considerable reduction in, or even elimination of contact shatter. At all times it will be seen that in switch units in accordance with the present invention, the armature is under positive loading by return spring forces and card forces, these forces tending to hold the armature against the stops adjacent the ends of the armature. Rebound is less than with a centre stop. In switch units as at present used it is possible for the armature to pivot about the centre stop to the extent that at least part of the armature may move a considerable distance toward the fully actuated position, thereby causing undesirable switching conditions, for example remaking or rebreaking of the hold off normal contacts.

What is claimed is:

l. A crossbar switch unit comprising:

a core having three legs, a centre leg and two outer legs;

an armature extending across said core adjacent the ends of said legs;

means flexibly mounting said armature on the end of said centre leg;

a coil mounted on said centre leg to move an armature from an inoperative position to an operative position; and I a stop member on each outer leg, each stop positioned to engagesaid annature on movement from said operative position to said inoperative position.

2. A crossbar switch unit as claimed in claim 1, each said stop member including a portion overlapping said armature.

3. A crossbar switch unit as claimed in claim 1', including an extension adjacent each end of said armature, said stop members overlapping said extensions.

4. A crossbar switch unit as claimed in claim 1, said means flexibly mounting said armature comprising a 

1. A crossbar switch unit comprising: a core having three legs, a centre leg and two outer legs; an armature extending across said core adjacent the ends of said legs; means flexibly mounting said armature on the end of said centre leg; a coil mounted on said centre leg to move an armature from an inoperative position to an operative position; and a stop member on each outer leg, each stop positioned to engage said armature on movement from said operative position to said inoperative position.
 2. A crossbar switch unit as claimed in claim 1, each said stop member including a portion overlapping said armature.
 3. A crossbar switch unit as claimed in claim 1, including an extension adjacent each end of said armature, said stop members overlapping said extensions.
 4. A crossbar switch unit as claimed in claim 1, said means flexibly mounting said armature comprising a leaf-spring. 